Conductivity measurement device

ABSTRACT

In some embodiments, the conductivity measurement device includes a conductivity probe, a solid state switch device, and a DC measurement circuit. The conductivity probe includes a first and second measurement pin used to measure a conductivity of the liquid. The solid state switch device is coupled to the conductivity probe and is configured to connect and disconnect the first measurement pin and second measurement pin to a first DC reference voltage and a second DC reference voltage. The DC measurement circuit is configured to generate a measurement signal such that the measurement signal is maintained at a first DC reference voltage and the first DC reference voltage is applied to the solid state switch device from the DC measurement circuit. In this manner, an alternating current (AC) voltage is applied to the measurement pins utilizing DC reference voltages, which helps to avoid contamination of the liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 17/142,965, filed on Jan. 6, 2021, which is basedupon and claims priority to U.S. Patent Application No. 63/071,064,filed on Aug. 27, 2020, both of which are incorporated herein byreference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be better understood with reference to the followingdrawings. The elements of the drawings are not necessarily to scalerelative to each other, emphasis instead being placed upon clearlyillustrating the principles of the disclosure. Furthermore, likereference numerals designate corresponding parts throughout the severalviews.

FIG. 1 is a block diagram of an embodiment of a conductivity measurementdevice.

FIGS. 2A-2C are circuit diagrams of another embodiment of a conductivitymeasurement device.

FIG. 3 is a circuit diagram of an embodiment of a voltage isolationcircuit.

FIG. 4 is a circuit diagram of an embodiment of a temperaturemeasurement circuit.

FIG. 5 is a flowchart of an embodiment of a method of measuring aconductivity of a liquid.

FIG. 6 is a high level block diagram of a processing system according toan embodiment.

DETAILED DESCRIPTION

The following disclosure provides different embodiments, or examples,for implementing features of the provided subject matter. Specificexamples of components, materials, values, steps, arrangements, or thelike, are described below to simplify the present disclosure. These are,of course, merely examples and are not limiting. Other components,materials, values, steps, arrangements, or the like, are contemplated.For example, the formation of a first feature over or on a secondfeature in the description that follows may include embodiments in whichthe first and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formed betweenthe first and second features, such that the first and second featuresmay not be in direct contact. In addition, the present disclosure mayrepeat reference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Conductivity measurement devices are used to measure the conductivity ofa liquid. In some embodiments, the conductivity measurement deviceincludes a conductivity probe, a solid state switch device, and a directcurrent (DC) measurement circuit. The conductivity probe includes afirst measurement pin and a second measurement pin placed in the liquidin order to measure conductivity. The solid state switch device iscoupled to the conductivity probe and is configured to connect anddisconnect the first measurement pin to a first DC reference voltage anda second DC reference voltage. Additionally, the solid state switchdevice is configured to connect and disconnect the second measurementpin to the first DC reference voltage and the second DC referencevoltage. The DC measurement circuit is configured to generate ameasurement signal such that the measurement signal is maintained at afirst DC reference voltage. The DC measurement circuit is coupled to thefirst solid state switch device such that the first DC reference voltageis applied to the solid state switch device from the DC measurementcircuit. In this manner, an alternating current (AC) voltage is appliedto the measurement pins utilizing DC reference voltages, which helps toavoid contamination of the liquid.

FIG. 1 is a circuit schematic of an example of a conductivitymeasurement device 100 for a liquid 101. The conductivity measurementdevice 100 is configured to measure the conductivity of the liquid 101and from the measurement determine the purity of the liquid (i.e.,degree of contamination of substances in the liquid 101). To make themeasurement, the conductivity measurement device 100 includes aconductivity probe 102 having a portion placed in the liquid 101. Theconductivity probe 102 may include a first measurement pin 104 and asecond measurement pin 106 for placement in the liquid 101. However, anysuitable configuration of a conductivity probe 102 may be utilizedincluding conductivity probes with a single pin or with more than twopins. After placement in the liquid 101, the conductivity measurementdevice 100 generates a test voltage TV across the measurement pins 104,106. By determining the current across the measurement pins 104, 106 asa result of the test voltage TV, the conductivity of the liquid 101 ismeasured and thus also the purity of the liquid 101. In otherembodiments, other electrical parameters may be detected in order todetermine the conductivity of the liquid including a voltage drop,differential measurements, and the like.

To prevent electroplating and to prevent ions from being released fromthe measurement pins 104, 106 into the liquid 101, the test voltage TVis applied as an AC voltage, such as a sinusoid, square wave, triangularwave, or another cyclical voltage or the like. However, as explained infurther detail below, the conductivity measurement device 100 generatesthe test voltage TV based on a DC voltage, which is a constant voltageother than for noise and variations due to non-ideal circuit behavior.

To generate the test voltage TV, the conductivity measurement device 100includes a solid state switch device 108 and a DC measurement circuit110. The solid state switch device may include one or more field effecttransistors, bipolar transistors, electromechanical switches, and/or thelike. The solid state switch device 108 is coupled to the conductivityprobe 102. In this specific embodiment, the solid state switch device108 is a multi-pole, multi-throw switch. Thus, the solid state switchdevice 108 has a pole switch terminal 112 connected to the firstmeasurement pin 104 and a pole switch terminal 114 connected to thesecond measurement pin 106. The solid state switch device 108 isconfigured to selectively connect and disconnect the pole switchterminals 112, 114 to throw switch terminals 118, 120.

The conductivity measurement device 100 includes control circuitry 122.In some embodiments, control circuitry 122 is optional. The test voltageTV repeats periodically every time cycle. During a first time intervalof each time cycle, a DC reference voltage VRef is applied to the firstmeasurement pin 104 and the DC reference voltage, e.g., a groundvoltage, is applied to the second measurement pin 106. During a secondtime interval of each time cycle, a DC reference voltage VRef is appliedto the second measurement pin 106 and the DC reference voltage, e.g., aground voltage, is applied to the first measurement pin 104. The firsttime interval and the second time interval repeat each time cycle. Insome embodiments, the first time interval extends for approximately 50percent of the time cycle and the second time interval extends forapproximately 50 percent of the time cycle. Other embodiments may applydifferent duty cycles depending on the characteristic of the desiredmeasurement. The control circuitry 122 is configured to selectivelyconnect the first measurement pin 104 to the throw switch terminal 118while selectively connecting the second measurement pin 106 to the throwswitch terminal 120 during a first time interval of a time cycle of thetest voltage TV. During a second time interval of the time cycle of thetest voltage TV, the control circuitry 122 is configured to selectivelyconnect the second measurement pin 106 to the throw switch terminal 118while selectively connecting the first measurement pin 104 to the throwswitch terminal 120. As explained in further detail below, this resultsin the test voltage TV being provided to the measurement pins 104, 106as an AC voltage even though DC voltages are generated by the DCmeasurement circuit 110. It should be noted that the control circuit 122may be provided as a general purpose computer implementing softwareconfigured to control the solid state switch device 108 and/or asspecialized hardware configured to control the solid state switch device108.

The DC measurement circuit 110 may be configured to generate ameasurement signal MS that indicates the conductivity of the liquid 101.In this particular embodiment, the measurement signal MS has ameasurement current that varies depending on the conductivity of theliquid 101. However, the DC measurement circuit 110 is configured togenerate the measurement signal MS such that the measurement signal MSis maintained at a DC reference voltage VRef. The DC measurement circuit110 is coupled to the solid state switch device 108 such that the DCreference voltage VRef is applied to the throw switch terminal 118 ofthe solid state switch device 108. In this manner, whichever one of thepole switch terminals 112, 114 is selectively connected to the poleswitch terminal 118 receives the DC reference voltage VRef while theother one of the pole switch terminals 114, 112 is selectivelydisconnected and does not receive the DC reference voltage VRef. Inother embodiments, the measurement signal MS may have a measurementvoltage or a differential parameter that varies depending on theconductivity of the liquid 101.

Additionally, the throw switch terminal 120 of the solid state switchdevice 108 is configured to receive a DC reference voltage VG that islower than the DC reference voltage VRef. In this particular embodiment,the DC reference voltage VG is a ground voltage. In other embodiments,the DC reference voltage VG may be a negative voltage. By having thethrow switch terminal 120 configured to receive the DC reference voltageVG, whichever one of the pole switch terminals 112, 114 is selectivelyconnected to the pole switch terminal 120 receives the DC referencevoltage VG. In some embodiments, the first DC reference voltage is theDC reference voltage VRef and the second DC reference voltage is the DCreference voltage VG.

Accordingly, when the control circuitry 122 alternates the selectiveconnection between the pole switch terminals 112, 114 and the throwswitch terminals 118, 120, the test voltage TV generates an AC voltagebetween the measurement pins 104, 106. This allows the conductivitymeasurement device 100 to maintain a stable voltage into the DCmeasurement circuit 110, while minimizing the electromagnetic feedbackeffect that the ultrapure water exhibits and minimizing the amount ofmaterial which migrates from the measurement pins 104, 106 into theliquid 101.

In this embodiment, the DC measurement device 110 includes anoperational amplifier 124, and an operational amplifier 126, and aresistor capacitor network 127. Other configurations of the DCmeasurement device 110 may be used. In this embodiment, the operationalamplifier 124 has an input terminal 128 (e.g., a non-inverting inputterminal), an input terminal 130 (e.g., an inverting input terminal),and an output terminal 132. The input terminal 128 is configured toreceive the DC reference voltage VRef. The output terminal 132 isconnected as feedback to the input terminal 130. As such, theoperational amplifier 124 is configured to generate the measurementsignal MS by driving the input terminal 130 to the DC reference voltageVRef. The input terminal 130 of the operational amplifier 124 isconnected to the throw switch terminal 118 of the solid state switchdevice 108. A feedback resistor 133 is coupled as feedback between theoutput terminal 132 and the input terminal 130 of the operationalamplifier 124. The feedback resistor 133 sets the measurableconductivity range of the DC measurement device 110.

In this embodiment, the operational amplifier 124 thus provides avoltage divider circuit where Vout=VRef(1+RF/RC), where RF is theresistance value of the feedback resistor 133 and RC is the resistancevalue of the liquid 101. Accordingly, the measurement signal MSindicates the conductivity of the liquid while providing an AC signalacross the measurement pins 104, 106 with the DC reference voltage VRef.This approach is much less noise prone particularly at the highresistances that may be present if the liquid 101 is water (resistancesranging from 6 Megohms to 18 Megohms).

The operational amplifier 124 is configured to generate the measurementsignal MS such that the current of the measurement signal MS varies inaccordance with the conductivity of the liquid 101 across themeasurement pins 104, 106. The operational amplifier 126 provides animpedance buffer as digital circuitry may have a much lower impedancethan the operational amplifier 124. The operational amplifier 126 has aninput terminal 140 (e.g., a non-inverting input terminal), an inputterminal 142 (e.g., an inverting input terminal), and an output terminal144. The input terminal 140 of the operational amplifier 126 isconnected to the output terminal 132 of the operational amplifier 124.Furthermore, the output terminal 144 of the operational amplifier 126 iscoupled as feedback to the input terminal 142 of the operationalamplifier 126. The operational amplifier 126 is thus configured toadjust the voltage to current ratio of the measurement signal MS toprovide impedance matching.

The resistor capacitor network 127 provides filtering with a timeconstant that is set in accordance with the time cycles of the testvoltage TV. In some embodiments, the time cycles of the test voltage TVare provided to be around 100 milliseconds (ms). In this embodiment, theresistor capacitor network 127 includes a resistor 146 connected inseries with the output terminal 144 and a capacitor 148 that isconnected in shunt. The DC measurement device 110 allows formeasurements to be taken very quickly since the voltages provided arestable and results in a reduced electroplating effect into the liquid101.

FIGS. 2A-2C are circuit schematics of an example of a conductivitymeasurement device 200 for a liquid 201. The conductivity measurementdevice 200 is configured to measure the conductivity of the liquid 201and from the measurement determine the purity of the liquid (i.e.,degree of contamination of substances in the liquid 201). To make themeasurement, the conductivity measurement device 200 includes aconductivity probe 202, a conductivity probe 250, and a conductivityprobe 256 that are each placed in the liquid 201. In this embodiment,the conductivity probe 202 includes a first measurement pin 204 and asecond measurement pin 206. The second conductivity probe 250 includes athird measurement pin 254 and a fourth measurement pin 252. Finally, thethird conductivity probe 256 includes a fifth conductivity pin 258 and asixth conductivity pin 260. When placed in the liquid 201, theconductivity measurement device 200 is configured to generate a testvoltage TV across the measurement pins 204, 206 of the conductivityprobe 202, the measurement pins 252, 254 of the conductivity probe 250,and/or the measurement pins 258, 260 of the conductivity probe 256. Bydetermining the current that results across the measurement pins 204,206, the measurement pins 252, 254, and/or the measurement pins 258, 260as a result of the test voltage TV, the conductivity of the liquid ismeasured and thus also the purity of the liquid 201. Otherconfigurations may include any number of conductivity probes less thanor more than 3.

To prevent electroplating and to prevent ions from being released fromthe measurement pins 204, 206, 252, 254, 258, 260, the test voltage TVis applied as an AC voltage, such as a sinusoid, square wave, triangularwave, or another cyclical voltage or the like. However, as explained infurther detail below, the conductivity measurement device 200 generatesthe test voltage TV from a DC voltage, which is a constant voltage otherthan for noise and variations due to non-ideal circuit behavior.

To generate the test voltage TV, the conductivity measurement device 200may include a solid state switch device 208 (FIG. 2B), a solid stateswitch device 209 (FIG. 2A), and a DC measurement circuit 210 (FIG. 2C).The solid state switch device 208 shown in FIG. 2B is coupled to theconductivity probe 202 (shown in FIG. 2A). In this specific embodiment,the solid state switch device 208 has a plurality of single pole singlethrow (SPST) switches. More specifically, the solid state switch device208 has a SPST switch between a pole switch terminal S1 and a throwswitch terminal D1, a pole switch terminal S2 and a throw switchterminal D2, a pole switch terminal S3 and a throw switch terminal D3, apole switch terminal S4 and a throw switch terminal D4, a pole switchterminal S5 and a throw switch terminal D5, a pole switch terminal S6and a throw switch terminal D6, a pole switch terminal S7 and a throwswitch terminal D7, and a pole switch terminal S8 and a throw switchterminal D8. The pole switch terminal S1 and the pole switch terminal S2are connected to the first measurement pin 204. The pole switch terminalS3 and a pole switch terminal S4 are connected to the second measurementpin 206.

In this specific embodiment, the solid state switch device 209 shown inFIG. 2A has a plurality of SPST switches. More specifically, the solidstate switch device 209 has a SPST switch between a pole switch terminalS1 and a throw switch terminal D1, a pole switch terminal S2 and a throwswitch terminal D2, a pole switch terminal S3 and a throw switchterminal D3, a pole switch terminal S4 and a throw switch terminal D4, apole switch terminal S5 and a throw switch terminal D5, a pole switchterminal S6 and a throw switch terminal D6, a pole switch terminal S7and a throw switch terminal D7, and a pole switch terminal S8 and athrow switch terminal D8. The pole switch terminal S1 and the poleswitch terminal S2 are connected to the fourth measurement pin 252. Thepole switch terminal S3 and a pole switch terminal S4 are connected tothe third measurement pin 254. The pole switch terminal S5 and the poleswitch terminal S6 are connected to the fifth measurement pin 258. Thepole switch terminal S7 and a pole switch terminal S8 are connected tothe sixth measurement pin 260.

In some embodiments, the conductivity measurement device 200 includescontrol circuitry 222 (shown in FIG. 2C). The control circuitry 222 isconfigured to selectively connect the first measurement pin 204 to thethrow switch terminal D1 of the solid state switch 208 while selectivelyconnecting the second measurement pin 206 to the throw switch terminalD4 of the solid state switch 208 during a first time interval of thetest voltage TV. Additionally, during the first time interval of thetest voltage TV, the control circuitry 222 is configured to selectivelyconnect the third measurement pin 254 to the throw switch terminal D1 ofthe solid state switch 209 while selectively connecting the fourthmeasurement pin 252 to the throw switch terminal D4 of the solid stateswitch 209. Finally, during the first time interval of the test voltageTV, the control circuitry 222 is configured to selectively connect thefifth measurement pin 258 to the throw switch terminal D5 of the solidstate switch 209 while selectively connecting the sixth measurement pin260 to the throw switch terminal D8 of the solid state switch 209.During a second time interval of the test voltage TV, the controlcircuitry 222 is configured to selectively connect the first measurementpin 204 to the throw switch terminal D2 of the solid state switch device208 while selectively connecting the second measurement pin 206 to thethrow switch terminal D3 of the solid state switch device 208.Additionally, during the second time interval of the test voltage TV,the control circuitry 222 is configured to selectively connect the thirdmeasurement pin 254 to the throw switch terminal D2 of the solid stateswitch device 209 while selectively connecting the fourth measurementpin 252 to the throw switch terminal D3 of the solid state switch device209. Finally, during the second time interval of the test voltage TV,the control circuitry 222 is configured to selectively connect the fifthmeasurement pin 258 to the throw switch terminal D6 of the solid stateswitch device 209 while selectively connecting the sixth measurement pin260 to the throw switch terminal D7 of the solid state switch device209. As explained in further detail below, this results in the testvoltage TV being provided to the measurement pins 204, 206 as an ACvoltage even though DC voltages are generated by the DC measurementcircuit 210. It should be noted that the control circuit 222 may be ageneral purpose computer implementing software to control the solidstate switch device 208 and/or specialized hardware.

The DC measurement circuit 210 shown in FIG. 2C is configured togenerate a measurement signal MS that indicates the conductivity of theliquid 201. In this particular embodiment, the measurement signal MS hasa measurement current that varies depending on the conductivity of theliquid 201. However, the DC measurement circuit 210 is configured togenerate the measurement signal MS such that the measurement signal MSis maintained at a DC reference voltage VRef. The DC measurement circuit210 is coupled to the solid state switch device 208 such that the DCreference voltage VRef is applied to the throw switch terminals D1, D3of the solid state switch device 208 and the throw switch terminals D1,D3, D5, D7 of the solid state switch device 209. In this manner,whichever one of the pole switch terminals S1, S3 of the solid stateswitch device 208 is selectively connected to either the throw switchterminal D1 or the throw switch terminal D3 of the solid state switchdevice 208 is the terminal that receives the DC reference voltage VRefwhile the other one of the pole switch terminals S3, S1 is selectivelydisconnected and does not receive the DC reference voltage VRef.Whichever one of the pole switch terminals S1, S3 of the solid stateswitch device 209 is selectively connected to either the throw switchterminal D1 or the throw switch terminal D3 of the solid state switchdevice 209 is the terminal that receives the DC reference voltage VRef.Whichever one of the pole switch terminals S5, S7 of the solid stateswitch device 209 is selectively connected to either the throw switchterminal D5 or the throw switch terminal D7 of the solid state switchdevice 209 is the terminal that receives the DC reference voltage VRef.

Additionally, the throw switch terminals D2, D4 of the solid stateswitch device 208 are configured to receive a DC reference voltage GNAthat is lower than the DC reference voltage VRef. In this particularembodiment, the DC reference voltage GNA is a ground voltage. In otherembodiments, the DC reference voltage GNA is a negative voltage. Byhaving the throw switch terminals D2, D4 of the solid state switchdevice 208 configured to receive the DC reference voltage GNA, whicheverone of the pole switch terminals S2, S4 of the solid state switch device208 is selectively connected to the throw switch terminals D2, D4 of thesolid state switch device 208 is the terminal that receives the DCreference voltage GNA.

The throw switch terminals D2, D4 of the solid state switch device 208are configured to receive a DC reference voltage GNA that is lower thanthe DC reference voltage VRef. In this particular embodiment, the DCreference voltage GNA is a ground voltage. In other embodiments, the DCreference voltage GNA is a negative voltage. By having the throw switchterminals D2, D4 of the solid state switch device 208 configured toreceive the DC reference voltage GNA, whichever one of the pole switchterminals S2, S4 of the solid state switch device 208 is selectivelyconnected to the throw switch terminals D2, D4 of the solid state switchdevice 208 is the terminal that receives the DC reference voltage GNA.

Furthermore, the throw switch terminals D2, D4 of the solid state switchdevice 209 are configured to receive a DC reference voltage GNA that islower than the DC reference voltage VRef. In this particular embodiment,the DC reference voltage GNA is a ground voltage. In other embodiments,the DC reference voltage GNA may be a negative voltage. By having thethrow switch terminals D2, D4 of the solid state switch device 209configured to receive the DC reference voltage GNA, whichever one of thepole switch terminals S2, S4 of the solid state switch device 209 isselectively connected to the throw switch terminals D2, D4 of the solidstate switch device 209 is the terminal that receives the DC referencevoltage GNA.

Additionally, the throw switch terminals D6, D8 of the solid stateswitch device 209 are configured to receive a DC reference voltage GNAthat is lower than the DC reference voltage VRef. In this particularembodiment, the DC reference voltage GNA is a ground voltage. In otherembodiments, the DC reference voltage GNA is a negative voltage. Byhaving the throw switch terminals D6, D8 of the solid state switchdevice 209 configured to receive the DC reference voltage GNA, whicheverone of the pole switch terminals S6, S8 of the solid state switch device209 is selectively connected to the throw switch terminals D6, D8 of thesolid state switch device 209 is the terminal that receives the DCreference voltage GNA.

Accordingly, the control circuitry 222 alternates the selectiveconnection between the pole switch terminals S1, S4 and the throw switchterminals D1, D4 of the solid state switch device 208 during one timeinterval of a time cycle and the pole switch terminals S2, S3 of thesolid state switch device 208 and the throw switch terminals D2, D3 ofthe solid state switch device 208 during another time interval of a timecycle. This results in the test voltage TV being an AC voltage betweenthe measurement pins 204, 206. The control circuitry 222 alternates theselective connection based on a timing configuration. The timingconfiguration determines the temporal length of each time interval inthe time cycle.

Furthermore, the control circuitry 222 alternates the selectiveconnection between the pole switch terminals S1, S4 and the throw switchterminals D1, D4 of the solid state switch device 209 during one timeinterval of a time cycle and the pole switch terminals S2, S3 of thesolid state switch device 209 and the throw switch terminals D2, D3 ofthe solid state switch device 209 during another time interval of a timecycle. This results in the test voltage TV being an AC voltage betweenthe measurement pins 250, 252.

Finally, the control circuitry 222 alternates the selective connectionbetween the pole switch terminals S5, S8 and the throw switch terminalsD5, D8 of the solid state switch device 209 during one time interval ofa time cycle and the pole switch terminals S6, S7 of the solid stateswitch device 209 and the throw switch terminals D6, D7 of the solidstate switch device 209 during another time interval of a time cycle.This results in the test voltage TV being an AC voltage between themeasurement pins 254, 256.

This allows the conductivity measurement device 200 to maintain a stablevoltage into the DC measurement circuit 210, while minimizing theelectromagnetic feedback effect that ultrapure water exhibits andminimizing the amount of material which migrates from the measurementpins 204, 206, 252, 254, 258, 260 into the liquid 201. Ultrapure waterhas a resistance in the range of 18 Megohms/cm at 25 Degrees C.

In this embodiment, the DC measurement device 210 includes anoperational amplifier 224, an operational amplifier 226, a resistorcapacitor network 228, and an analog to digital converter 231. Theoperational amplifier 224 has an input terminal 229 (e.g., anon-inverting input terminal), an input terminal 230 (e.g., an invertinginput terminal), and an output terminal 232. The input terminal 229 isconfigured to receive the DC reference voltage VRef. The output terminal232 is connected as feedback to the input terminal 230. As such, theoperational amplifier 224 is configured to generate the measurementsignal MS by driving the input terminal 230 to the DC reference voltageVRef. The input terminal 230 of the operational amplifier 224 isconnected to the throw switch terminals D1, D3 of the solid state switchdevice 208 and the throw switch terminals D1, D3, D5, D7 of the solidstate switch device 209.

The conductivity measurement device 200 also includes resistors233A-233D, where each of the resistors 233A-233D has a differentresistance value. The output terminal 232 is connected to the throwswitch terminals D5-D8 of the solid state switch device 208.Additionally, the resistor 233A is connected to between the pole switchterminal S5 of the solid state switch device 208 and the input terminal230 of the operational amplifier 224. The resistor 233B is connectedbetween the pole switch terminal S6 of the solid state switch device 208and the input terminal 230 of the operational amplifier 224. Theresistor 233C is connected between the pole switch terminal S7 of thesolid state switch device 208 and the input terminal 230 of theoperational amplifier 224. The resistor 233D is connected between thepole switch terminal S8 of the solid state switch device 208 and theinput terminal 230 of the operational amplifier 224. The solid stateswitch device 208 is further configured to selectively connect any oneof the resistors 233A-233D as feedback between the output terminal 232and the second input terminal of the operational amplifier 224. In thismanner, the solid state switch device 208 allows for the controlcircuitry 222 to select the measurable conductivity range of theconductivity measurement device 200. In this particular embodiment, theresistor 233A has a resistance value 5 Megohms, the resistor 233B has aresistance value of 1 Megohms, the resistor 233C is 470 kilohms, and theresistor 233D has a resistance value of 100 kilohms.

The operational amplifier 224 thus provides a voltage driver circuitwhich results in the voltage across the conductivity probe 202 having amagnitude equal to VRef while still providing an AC signal across themeasurement pins 204, 206, 252, 254, 258, 260. This approach is muchless noise prone particularly at the high resistances that may bepresent if the liquid 201 is water (resistances between 6 Megohms-18Megohms).

The operational amplifier 224 is configured to generate the measurementsignal MS such that the measurement current of the measurement signal MSvaries in accordance with the conductivity of the liquid 201 across themeasurement pins 204, 206, the measurement pins 252, 254, and/or themeasurement pins 258, 260. The operational amplifier 226 provides animpedance buffer to the digital converter 231 which has a much lowerinput impedance than the operational amplifier 224. The operationalamplifier 226 has an input terminal 240 (e.g., a non-inverting inputterminal), an input terminal 242 (e.g., an inverting input terminal),and an output terminal 244. The input terminal 240 of the operationalamplifier 226 is connected to the output terminal 232 of the operationalamplifier 224. Furthermore, the output terminal 244 of the operationalamplifier 226 is coupled as feedback to the input terminal 242 of theoperational amplifier 224. The operational amplifier 226 is thusconfigured to adjust the voltage to current ratio of the measurementsignal MS to provide impedance matching.

The resistor capacitor network 228 provides filtering with a timeconstant set in accordance with the time cycles of the test voltage TV.In some embodiments, the time cycles of the test voltage TV are providedto be around 100 ms. In this embodiment, the resistor capacitor network228 includes a resistor 246 connected in series with the output terminal244 and a capacitor 248 that is connected in shunt. In this particularembodiment, the resistor 246 has a resistance value of 2 kilohmsand thecapacitor has a capacitance value of 4.7 microfarads. The DC measurementdevice 210 allows for measurements to be taken very quickly since thevoltages provided are stable and result in a reduced electroplatingeffect.

The analog to digital converter 231 is configured to compare themeasurement signal to the DC reference voltage VRef so as to generatedigital conductivity measurement that identifies the conductivity of theliquid 201. In some embodiments, the analog to digital converter 231compares VRef to the measurement signal MS and uses ratios to determinethe conductivity. This cancels out thermal effects which could causemeasurement errors.

FIG. 3 is a circuit diagram of an embodiment of a voltage isolationcircuit 300. The voltage isolation circuit 300 is configured to generatethe power source voltage VDD from a power source that generates a 24Volt signal. The power source voltage may come from a battery or an ACto DC converter. The voltage isolation circuit 300 isolates the DCreference voltage GND to prevent noise from causing the pins tocontaminate the liquid. It should be noted that other configurations ofa voltage isolation circuit 300 may be utilized to generate the powersource voltage VDD.

FIG. 4 is a circuit diagram of an embodiment of a temperaturemeasurement circuit 400. The temperature measurement circuit 400 isconfigured to generate measurement signals TS that indicate atemperature of the liquid 201. Because conductivity of a liquid, such aswater, varies, the control circuit 222 may utilize the measurementsignal TS to make an appropriate measurement of the water from themeasurement signal MS. The temperature measurement circuit 400 includesthree op-amps U34, U24, and U14. The op amp U34 is in an integratorconfiguration and measures the temperature of the liquid being tested bythe conductivity probe 202. A buffer op amp U38 performs impedancematching with a measurement circuit 402. Additionally, the op amp U24 isin an integrator configuration and measures the temperature of theliquid being tested by the conductivity probe 250. A buffer op amp U28performs impedance matching with a measurement circuit 402. Finally, theop amp U14 is in an integrator configuration and measures thetemperature of the liquid being tested by the conductivity probe 256. Abuffer op amp U18 performs impedance matching with a measurement circuit402. The measurement circuit 402 compares the integrated voltage withthe reference voltage VRef, which gives a measurement of thetemperature. It should be noted that other configurations of thetemperature measurement circuit 400 may be utilized in order to measurethe temperature of the liquid 201.

FIG. 5 is a circuit diagram of an embodiment of a method of measuring aconductivity of a liquid. In some embodiments, a first measurement pinand a second measurement pin are positioned in the liquid (procedure500). A first DC reference voltage is applied to the first measurementpin and a second DC reference voltage is applied to the secondmeasurement pin during a first time period (procedure 502). In someembodiments, procedure 502 includes operating a solid state switchdevice to selectively connect the first measurement pin to receive thefirst DC reference voltage from the DC measurement circuit, andoperating the solid state switch device to selectively connect thesecond measurement pin to receive the second DC reference voltage.

Then, the first DC reference voltage is applied to the secondmeasurement pin and a second DC reference voltage is applied to thefirst measurement pin during a second time period (procedure 504). Insome embodiments, procedure 504 includes operating the solid stateswitch device to selectively connect the second measurement pin toreceive the first DC reference voltage from the DC measurement circuit,and operating the solid state switch device to selectively connect thefirst measurement pin to receive the second DC reference voltage. Byrepeating procedures 502, 504, an AC voltage is applied across the firstmeasurement pin and the second measurement pin with DC referencevoltages.

FIG. 6 is a block diagram of a general purpose computing device 600 inaccordance with some embodiments. The computing device 600 is configuredto generate operate as described above with respect to the controlcircuitry 122 in FIG. 1 or the control circuitry 222 in FIG. 2 . Thegeneral purpose computing device 600 also operates the solid stateswitch device so that the solid state switch device performs operations502, 504.

In some embodiments, computing device 600 is a general purpose computingdevice including at least one hardware processor 602 and anon-transitory, computer-readable storage medium 604. Storage medium604, amongst other things, is encoded with, i.e., stores, computerprogram code 606, i.e., a set of computer-executable instructions.Execution of instructions 606 by hardware processor 602 that implementsa portion or all of the methods described herein in accordance with oneor more embodiments (hereinafter, the noted processes and/or methods).Storage medium 604, amongst other things computer program code 606.

Processor 602 is electrically connected to computer-readable storagemedium 604 via a bus 608. Processor 602 is also electrically connectedto an I/O interface 610 by bus 608. A network interface 612 is alsoelectrically connected to processor 602 via bus 608. Network interface612 is connected to a network 614, so that processor 602 andcomputer-readable storage medium 604 are capable of connecting toexternal elements via network 614. Processor 602 is configured toexecute computer program code 606 encoded in computer-readable storagemedium 604 in order to cause system 600 to be usable for performing aportion or all of the noted processes and/or methods. In one or moreembodiments, processor 602 is a central processing unit (CPU), amulti-processor, a distributed processing system, an applicationspecific integrated circuit (ASIC), and/or a suitable processing unit.

In one or more embodiments, computer-readable storage medium 604 is anelectronic, magnetic, optical, electromagnetic, infrared, and/or asemiconductor system (or apparatus or device). For example,computer-readable storage medium 604 includes a semiconductor orsolid-state memory, a magnetic tape, a removable computer diskette, arandom access memory (RAM), a read-only memory (ROM), a rigid magneticdisk, and/or an optical disk. In one or more embodiments using opticaldisks, computer-readable storage medium 604 includes a compact disk-readonly memory (CD-ROM), a compact disk-read/write (CD-R/W), and/or adigital video disc (DVD).

In one or more embodiments, storage medium 604 stores computer programcode 606 configured to cause computing device 600 (where such executionrepresents (at least in part) the EDA tool) to be usable for performinga portion or all of the noted processes and/or methods. In one or moreembodiments, storage medium 604 also stores information whichfacilitates performing a portion or all of the noted processes and/ormethods.

Computing device 600 includes I/O interface 610. I/O interface 610 isconnected to external circuitry. In one or more embodiments, I/Ointerface 610 includes a keyboard, keypad, mouse, trackball, trackpad,touchscreen, and/or cursor direction keys for communicating informationand commands to processor 602.

Computing device 600 also includes network interface 612 connected toprocessor 602. Network interface 612 allows computing device 600 tocommunicate with network 614, to which one or more other computersystems are connected. Network interface 612 includes wireless networkinterfaces such as BLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA; or wirednetwork interfaces such as ETHERNET, USB, or IEEE-1364. In one or moreembodiments, a portion or all of noted processes and/or methods, isimplemented in two or more systems 600.

Computing device 600 is configured to receive information through I/Ointerface 610. The information received through I/O interface 610includes one or more of instructions, data, and/or other parameters forprocessing by processor 602. The information is transferred to processor602 via bus 608. Computing device 600 is configured to receiveinformation related to a UI through I/O interface 610. The informationis stored in computer-readable medium 604 as user interface (UI) 642.

In some embodiments, a portion or all of the noted processes and/ormethods is implemented as a standalone software application forexecution by a processor. In some embodiments, a portion or all of thenoted processes and/or methods is implemented as a software applicationthat is a part of an additional software application. In someembodiments, a portion or all of the noted processes and/or methods isimplemented as a plug-in to a software application. In some embodiments,a portion or all of the noted processes and/or methods is implemented asa software application that is used by computing device 600.

In some embodiments, the processes are realized as functions of aprogram stored in a non-transitory computer readable recording medium.Examples of a non-transitory computer readable recording medium include,but are not limited to, external/removable and/or internal/built-instorage or memory unit, e.g., one or more of an optical disk, such as aDVD, a magnetic disk, such as a hard disk, a semiconductor memory, suchas a ROM, a RAM, a memory card, and the like.

In some embodiments, a conductivity measurement device for a liquid,includes a first conductivity probe comprising a first measurement pinand a second measurement pin and a first solid state switch devicecoupled to the first conductivity probe. The first solid state switchdevice is configured to selectively connect and disconnect the firstmeasurement pin to a first DC reference voltage and a second DCreference voltage and selectively connect and disconnect the secondmeasurement pin to the first DC reference voltage and the second DCreference voltage. Additionally, the conductivity measurement devicefurther includes a DC measurement circuit configured to generate ameasurement signal such that the measurement signal is maintained at afirst DC reference voltage, wherein the DC measurement circuit iscoupled to the first solid state switch device such that the first DCreference voltage is applied to the first solid state switch device fromthe DC measurement circuit.

In some embodiments, a method of measuring a conductivity of a liquid,includes providing a first measurement pin and a second measurement pinin the liquid, applying a first DC reference voltage to the firstmeasurement pin and a second DC reference voltage to the secondmeasurement pin during a first time period, and applying the first DCreference voltage to the second measurement pin and the second DCreference voltage to the first measurement pin during a second timeperiod.

In some embodiments, a conductivity measurement device for a liquid,includes a first conductivity probe comprising a first measurement pinand a second measurement pin, a first solid state switch device coupledto the first conductivity probe, the first solid state switch devicehaving a first switch terminal and a second switch terminal, and a DCcircuit configured to generate a first DC reference voltage, wherein theDC circuit is coupled to the first solid state switch device such thatthe first DC reference voltage is applied to the first switch terminalof the first solid state switch device. The first solid state switchdevice is configured to selectively connect and disconnect the firstmeasurement pin to the first switch terminal and the second switchterminal and selectively connect and disconnect the second measurementpin to the first switch terminal and the second switch terminal.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

Now, therefore, the following is claimed:
 1. A method of measuring aconductivity of a liquid, comprising: providing a first measurement pinand a second measurement pin in the liquid; applying a first DCreference voltage to the first measurement pin and a second DC referencevoltage to the second measurement pin during a first time period; andapplying the first DC reference voltage to the second measurement pinand the second DC reference voltage to the first measurement pin duringa second time period.
 2. The method of claim 1, wherein the first DCreference voltage is greater than the second DC reference voltage. 3.The method of claim 2, wherein the second DC reference voltage is aground voltage.
 4. The method of claim 1, wherein: applying a first DCreference voltage to the first measurement pin and a second DC referencevoltage to the second measurement pin during a first time periodcomprises: generating the first DC reference voltage with a DCmeasurement circuit; operating a solid state switch device toselectively connect the first measurement pin to receive the first DCreference voltage from the DC measurement circuit; and operating thesolid state switch device to selectively connect the second measurementpin to receive the second DC reference voltage.